Microfluidic devices are becoming an important component of instrumentation in many areas of technology including, for example, chemical synthesis and analysis. Conventionally, channels for fluid flow in microfluidic devices are machined, etched, or molded into a planar substrate. The channels are then enclosed by attaching a second substrate. These channels can be filled with various liquids used for chemical processing or with a gel used for electrophoric separations, for example.
In order to perform more general chromatography in this same device, it is necessary to incorporate a stationary phase within the channels. This can be done by directly etching chromatographic supports into the channels. However, it is not possible with current technology to easily etch supports with cross sections large enough and pore sizes small enough for high performance liquid chromatography (HPLC). Further, the surface of the supports must be derivatized after they are enclosed by the second substrate. Since the surface of the supports cannot be derivatized before enclosure, supports with different surface chemistries must be derivatized individually. This increases manufacturing costs and decreases production yield.
Alternatively, a stationary phase can be incorporated by packing open conduits with chromatographic porous particles, silica, for example, or a castable porous polymer. However, packing a channel with a single porous material is fairly difficult and is thus subject to poor manufacturing yield. It is even more difficult to pack two different materials into a channel or channels that are in fluidic communication.
Methods of fabricating microfluidic structures in the prior art include: U.S. Pat. Nos. 6,074,725, 6,156,273 and 6,176,962. These methods suffer from the aforementioned disadvantages.
Accordingly, there is a need to easily and inexpensively incorporate surface derivatized porous materials having a pore size small enough for HPLC and for high-pressure electrokinetic devices into a single micro-flow device. There is also a need to incorporate more than one porous material into a single micro-flow device.